Casing impairment induced by shear slip along a weak layer in shale due to fluid (steam) injection

Thermal recovery processes such as cyclic steam stimulation and steam assisted gravity drainage involve large volume fluid and steam injection into oil sand reservoirs. Thermal expansion and dilatation of oil sand formation causes horizontal and vertical displacements in the overburden. These deformations may not exert detrimental effects on casings and facilities if the deformation properties of the overburden are homogeneous without drastic local variation along depth. However, if there exists some natural (clay seams) or induced weak layers (swollen and softened shale layer), shear slip could develop along these discontinuities, thereby impairing the nearby casings and facilities. This paper develops a semi-empirical analytical method for estimating the relative shear slip along a weak layer in shale due to fluid and steam injection. The magnitude of slip depends on the volume and distribution of fluid and steam injection, and the extent and location of the weak layer. Calculated results demonstrate that the shear slip along the weak layer could impose concerns regarding the steaming strategy and environmental protection.